I have more than 1 corner, is that also possible?

The same goes for this situation, you can order the splashback on the total dimensions of the back wall and cut to size in the corners. If you need to do a lot of cutting it might be a good idea to add a small margin to the order (in case you cut wrong or the corners aren’t 100% straight). Again, place a remark on the order form if you want us to take it into account when making the design for your splashback.